Loading...

Biomechanical Effects of Intervertebral Disc Nucleotomy Surgery on Adjacent Joints Using a Coupled Musculoskeletal Finite Element Model

Haghighi, Ali | 2024

0 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57600 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Arjmand, Navid
  7. Abstract:
  8. According to studies, low back pain is one of the most common and costly musculoskeletal disorders. Herniation of intervertebral discs exerts pressure on the nerves, causing pain. To alleviate this, physicians perform a procedure called nucleotomy, which removes the disc's nucleus pulposus to reduce pressure, retract the disc, and relieve pain. Accurate estimation of spinal forces during activities is essential for injury prevention, activity correction, and improved surgical techniques. Although laboratory studies on humans or cadavers are valid, they are often invasive and limited to simple scenarios, necessitating precise computational models for comprehensive biomechanical analysis. Biomechanical models are classified into finite element models, musculoskeletal models, and hybrid models. Passive finite element models neglect muscle functions, while active musculoskeletal models poorly simulate vertebrae and discs, limiting their ability to predict disc stiffness. The "gold standard" model is the fully coupled finite element–musculoskeletal model, integrating both passive structures and active muscles. This model uses optimization techniques to calculate muscle forces, iteratively applying them to the finite element model until convergence. In this study, a coupled spine model with a nucleotomized L4-L5 disc is developed. To simulate this surgical procedure, a zero-pressure condition is applied within the nucleus pulposus of the operated disc. Due to the reduced height of the operated disc, the rotation of the L5 vertebra changes, which is determined by minimizing the reaction moment of the operated section and the total muscle force. After developing the coupled nucleotomized model, test scenarios including standing and forward bending at 20, 40, and 60 degrees were simulated, and the model's kinematics (vertebral angles) were analyzed. The experimental outputs include nucleus pulposus pressures, muscle and ligament forces, and compressive and shear forces on the discs and facet joints. To prevent an overload of results, only the operated section and the two adjacent sections were analyzed. The nucleotomy model's results were compared with those of a healthy model under similar conditions. Findings revealed that post-nucleotomy, the nucleus pulposus pressure in the operated disc dropped to zero, with a maximum pressure reduction of 9.9% in adjacent discs. The total local muscle forces increased post-surgery (average increase of 38.9%), while disc forces generally decreased, especially during greater flexion angles (maximum reduction of 7.7%). However, the facet joint in the operated section experienced a significant increase in both compressive (average increase of 434%) and shear forces (average increase of 198%), aligning well with experimental results. This increase contributed to a reduction in ligament forces during 40° and 60° flexion (73.7% and 48.6% reductions, respectively, in the operated section). Finally, stress distribution contours on the operated disc and its two adjacent discs were examined, revealing a significant increase in stress within the annulus fibrosus of the operated disc (average increase of 2.6 times), particularly in the anterior region during greater flexion angles. These findings suggest that modifications to the nucleotomy procedure—such as applying constraints to control post-operative kinematics or replacing the nucleus pulposus with an artificial nucleus—could improve the surgery's quality and effectiveness. It is hoped that this research represents a small step in that direction
  9. Keywords:
  10. Spine ; Finite Element Modeling ; Coupled Musculoskeletal Finite Element Modeling ; Optimization ; Nucleotomy Surgery ; Adjacent Segment Disease (ASD)

 Digital Object List

 Bookmark

...see more